<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var a = 5;
        var b = 5;
        /* a = b = 5; */
        if(a === b){
            b = 10;
            alert(b);
        }

        var x = 80;
        if(x < 17 && x <= 17){
            alert("你还未成年")
        }else if(x < 30 && x <= 30){
            alert("你已经中年了")
        }else if(x > 60 && x <= 80){
            alert("你已经退休了")
        }else(
            alert(1234)
        )

        var b = 60;
        if(b >= 60){
            alert("你已经退休了")
        }else if(b > 30){
            alert("你已经中年了")
        }else if( b > 18){
            alert("你已经成年了")
        }else{
            alert("你还未成年")
        }
    </script>
</body>
</html>